As the progress of the precision of optical analysis material, Raman spectra is developed as a popular optical and material analysis method. The samples of Raman spectra are low population and prepared easily and fast. Raman spectra would not destroy the samples. GaN is an ideal blue light substrate and a popular nitrogen compound of semi-conductor in III-V group . The character of the GaN is it has a wild direct band gas, high thermal conductivity and high chemical stability. This study is focus on analyzing if there is any difference of the structure of GaN growing on the different substrates. It is compared with photoluminescence spectrum to make sure the accuracy of the result of Raman spectra.

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Arsenic (As) undergoes extensive metabolism in biological systems involving numerous metabolites with varying toxicities. It is important to obtain reliable information on arsenic speciation for understanding toxicity and relevant modes of action. Currently, popular arsenic speciation techniques, such as chromatographic/electrophoretic separation following extraction of biological samples, may induce the alternation of arsenic species during sample preparation. The present study was aimed to develop novel arsenic speciation methods for biological matrices using surface-enhanced Raman spectroscopy (SERS), which, as a rapid and non-destructive photon scattering technique. The use of silver nanoparticles with different surface coating molecules as SERS substrates permits the measurement of four common arsenicals, including arsenite (AsIII), arsenate (AsV), monomethylarsonic acid (MMAV) and dimethylarsinic acid (DMAV). This speciation was successfully carried out using positively charged nanoparticles, and simultaneous detection of arsenicals was achieved. Secondly, arsenic speciation using coffee ring effect-based separation and SERS detection was explored on a silver nanofilm (AgNF), which was prepared by close packing of silver nanoparticles (AgNPs) on a glass substrate surface. Although arsenic separation using the conventional coffee ring effect is difficult because of the limited migration distance, a halo coffee ring was successfully developed through addition of surfactants, and was shown to be capable of arsenicals separation. The surfactants introduced in the sample solution reduce the surface tension of the droplet and generate strong capillary action. Consequently, solvent in the droplet migrated into the peripheral regions and the solvated arsenicals to migrated varying distances due to their differential affinity to AgNF, resulting in a separation of arsenicals in the peripheral region of the coffee ring. Finaly, a method combining experimental Raman spectra measurements and theoretical Raman spectra simulations was developed and employed to obtain Raman spectra of important and emerging arsenic metabolites. These arsenicals include monomethylarsonous acid (MMAIII), dimethylarsinous acid (DMAIII), dimethylmonothioarinic acid (DMMTAV), dimethyldithioarsinic acid (DMDTAV), S-(Dimethylarsenic) cysteine (DMAIIICys) and dimethylarsinous glutathione (DMAIIIGS). The fingerprint vibrational frequencies obtained here for various arsenicals, some of which have not reported previously, provide valuable information for future SERS detection of arsenicals.

No / Raman spectra of an extremophile cyanobacterial colony in hydromagnesite from Lake Salda in Turkey have revealed a biogeological modification which is manifest as aragonite in the stratum associated with the colony. The presence of key spectral biomarkers of organic protectant molecules such as (8-carotene and scytonemin indicate that the survival strategy of the cyanobacteria is significantly one of UV-radiation protection. The terrestrial location of this extremophile is worthy of consideration further because of its possible putative link with the White Rock formations in Sabaea Terra and Juventae Chasma on Mars.

Infrared reflectivity and transmittance measurements (200-5000 cm⁻¹) were carried out on heavily-doped GaAs:C films grown by molecular beam epitaxy. With increasing carbon concentration, a broad reflectivity minimum develops in the 1000-3000 cm⁻¹ region and the one-phonon band near 270 cm⁻¹ rides on a progressively increasing high-reflectivity background. An effective-plasmon/one-phonon dielectric function with only two free parameters (plasma frequency ω_p and damping constant γ_p) gives a good description of the main features of the reflectivity spectra. The dependence of effective plasma frequency on hole concentration p is linear. At each doping, the effective-plasmon damping constant γ_p is large and corresponds to an optical hole mobility that is about half the Hall mobility at that p. Secondary-ion mass spectroscopy and localized-vibrational-mode measurements indicate that the Hall-effect-derived hole concentration is close to the carbon concentration and that the Hall factor is close to unity, so that the Hall mobility provides a good estimate of the actual dc mobility. Also, analysis shows that, for our highly-doped samples, the observed dichotomy between the dc and infrared mobilities is not a statistical-averaging artifact of the approximations involved in the model. The explanation of the small infrared mobility resides in the influence of intervalence band absorption on the effective-plasmon fit, which operationally defines that mobility via the effective-plasmon damping. The optical properties obtained with the use of the effective-plasmon model for GaAs:C yield a phenomenological, approximate, overall picture of the infrared spectra. But the neglect of intervalenceband transitions, for this p-type semiconductor, is shown (in this dissertation) to be a serious drawback of this simple model. In order to obtain the optical properties of GaAs:C in a model-independent way, and to attempt to resolve the apparent dc/infrared mobility dichotomy, we made use of a recently-developed spectroscopic-analysis procedure. Using direct numerical-solution techniques for the reflectance (R) and transmittance (T) equations of a multilayer structure, we analyzed our infrared R and T results for highly-doped films having hole concentrations from 2 × 10¹⁹ up to 1.4 × 10²⁰ cm⁻³. The optical properties were determined for photon energies from 0.07 to 0.6 eV, in which region plasmon (intraband) and intervalenceband contributions are in competition. Our results for the optical absorption coefficient resolve two separate peaks located (at high doping) at about 0.1 and 0.2 eV. (The effective-plasmon model necessarily missed the two-peak character of the actual absorption spectrum.) By carrying out theoretical calculations of the intervalenceband (IVB) absorption processes for our dopings, we identify the peak near 0.2 eV with light-hole to heavy-hole IVB transitions, and we attribute the lower-energy peak to the hole plasmon. Our experimental absorption spectra are very well described by a model combining the intervalenceband contribution to the dielectric function with a plasmon contribution. The hole-plasmon parameters ω_plasmon and γ_plasmon that we obtain for highly-doped p-GaAs yield an infrared mobility which (unlike the too-small IVB-entangled infrared mobility implied by the use of the usual effective-plasmon model) is in substantial agreement with the dc mobility. Therefore, in actuality, there is no dc/infrared mobility discrepancy. The discrepancy implied by the use of the usual, standard-operating-procedure, effective-plasmon model is a consequence of the inadequacy of that model for p-type semiconductors exhibiting intervalenceband infrared absorption. Raman-scattering measurements were carried out on the GaAs:C films. Only the phononlike coupled plasmon-phonon mode is observed. The non-occurrence of the plasmonlike mode is due to the large damping of the hole plasmon and the competition with strong Raman scattering by intervalenceband transitions among the heavy-hole, light-hole, and split-off bands. Analysis of the phononlike coupled mode, within the framework of the wavevector-dependent Lindhard-Mermin dielectric function, supports the hole properties that we determined by Hall and infrared studies. Photoluminescence measurements showed that the split-off band also participates in the photoluminescence of GaAs:C, giving rise to an above-bandgap emission band corresponding to transitions from the conduction band to the split-off valence band. / Ph. D.

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No description available.

This thesis addresses the issue of a potential future microelectronics technology, namely the possibility of utilising the optical properties of nanocrystalline silicon for optoelectronic circuits. The subject is subdivided into three chapters. Chapter 1 is an introduction. It formulates the oncoming problem for microelectronic development, explains the basics of Integrated Optoelectronics, introduces porous silicon as a new light-emitting material and gives a brief review of other competing light-emitting material systems currently under investigation. Examples of existing porous silicon devices are given. Chapter 2 reviews the basic physics relevant to the subject of this thesis and informs on the present situation in this field of research, including both experimental and theoretical knowledge gained up-to-date. The chapter provides the necessary background for correct interpretation of the results reported in Chapter 3 and for a realistic decision on the direction for future work. Chapter 3 describes my own experimental and computational results within the framework of the subject, obtained at De Montfort University. These include: onestep preparation of laterally structured porous silicon with photoluminescence and microscopy characterisation, Raman spectroscopy of porous silicon, a polarisation study of the photoluminescence from porous silicon, computer simulations of the conductivity of two-component media and of laser focused atomic deposition for nanostructure fabrication. Thus, this thesis makes a dual contribution to the chosen field: it summarises the present knowledge on the possibility of utilising optical properties of nanocrystalline silicon in silicon-based electronics, and it reports new results within the framework of the subject. The main conclusion is that due to its promising optoelectronic properties nanocrystalline silicon remains a prospective competitor for the cheapest and fastest microelectronics of the next century.

Polyyne molecules were produced as a result of the femtosecond laser irradiation of liquid acetone (CH3)2CO and alkane molecules hexane C6H14 and octane C8H18 using 800 nm, 100 fs duration pulses. These polyynes have been detected as a Raman band in irradiated liquid from 1800 to 2200 cm−1. Polyyne molecules generally detected as a Raman band in SERS experiment are C8H2, C10H2, C12H2 and C14H2. Two well established experimental techniques, time of flight mass spectrometry and surface enhanced Raman spectrometry were used to identify positively polyyne formation as a result of femtosecond laser irradiation of acetone and alkane liquids. Small polyynes C2H2, C4H2, and C6H2 were positively detected in the time of flight mass spectrometer TFMS, while longer polyynes from C6H2, C8H2, C10H2, C12H2 and C14H2 were detected by surface enhanced Raman spectroscopy SERS. Intensity capping occurs in a liquid due to filamentation, and the resulting intensity in a liquid is s 1013 W/cm2 during irradiation. This results in main process of ionization in the larger part of the laser focus as multiphoton ionization MPI. Focal volume increase in a liquid provides a larger volume where ions C+, C+2 and C2+are produced to initiate chemical reactions outside the laser focus. The current work established positively, that the longer polyyne formation does not occur by dehydrogenation of alkane molecules by only breaking the C-H bonds as was previously anticipated. It is proposed in this work that lengthening of polyyne chains occurs due to addition reaction of species of C+, C+2 and C2+ to double bonded species themselves produced as a result of the breaking down of the parent molecules in the laser focus. The carbon addition reactions occur outside the laser focus due to the close proximity of molecules in the liquid phase.

Polyyne molecules were produced as a result of the femtosecond laser irradiation of liquid acetone (CH3)2CO and alkane molecules hexane C6H14 and octane C8H18 using 800 nm, 100 fs duration pulses. These polyynes have been detected as a Raman band in irradiated liquid from 1800 to 2200 cm−1. Polyyne molecules generally detected as a Raman band in SERS experiment are C8H2, C10H2, C12H2 and C14H2. Two well established experimental techniques, time of flight mass spectrometry and surface enhanced Raman spectrometry were used to identify positively polyyne formation as a result of femtosecond laser irradiation of acetone and alkane liquids. Small polyynes C2H2, C4H2, and C6H2 were positively detected in the time of flight mass spectrometer TFMS, while longer polyynes from C6H2, C8H2, C10H2, C12H2 and C14H2 were detected by surface enhanced Raman spectroscopy SERS. Intensity capping occurs in a liquid due to filamentation, and the resulting intensity in a liquid is s 1013 W/cm2 during irradiation. This results in main process of ionization in the larger part of the laser focus as multiphoton ionization MPI. Focal volume increase in a liquid provides a larger volume where ions C+, C+2 and C2+are produced to initiate chemical reactions outside the laser focus. The current work established positively, that the longer polyyne formation does not occur by dehydrogenation of alkane molecules by only breaking the C-H bonds as was previously anticipated. It is proposed in this work that lengthening of polyyne chains occurs due to addition reaction of species of C+, C+2 and C2+ to double bonded species themselves produced as a result of the breaking down of the parent molecules in the laser focus. The carbon addition reactions occur outside the laser focus due to the close proximity of molecules in the liquid phase.